A welding gun includes a stationary gun arm and a movable gun arm on which electrode tips are provided on respective distal ends thereof. The movable gun arm is capable of approaching toward and moving away from the stationary gun arm under an action of a motor and a ball screw or the like, and an opening and closing operation is carried out by such separation from and approaching toward the stationary gun arm.
More specifically, the stationary gun arm is retained in a positioned and fixed state by a retaining unit in which guide grooves are formed. On the other hand, the movable gun arm is retained in the retaining unit through an arm holder. Rollers are disposed on the arm holder, and the rollers are inserted slidably in the guide grooves that are formed in the retaining unit. Thus, accompanying the motor being energized and the ball screw starting to undertake a rotating operation, the arm holder swings together with the rollers sliding inside the guide grooves. As a result, the movable gun arm swings. In addition, when the movable gun arm approaches toward the stationary gun arm, the electrode tips face toward one another and welding is carried out with respect to a member to be welded.
In relation to the aforementioned structure and operations, detailed descriptions thereof are given in Japanese Utility Model Publication No. 58-023492 and Japanese Laid-Open Patent Publication No. 2012-035274.